Several shots show the corner of Bleecker Street and the Bowery. The street signs have white letters on a green background. In the 1970s, Manhattan street signs had black letters on a yellow background.
Songs played in the movie by The Ramones, are Spirit in My House and I Got Knocked Down (But I'll Get Up) recorded by Joey Ramone in 2000 and 2001, 32 years after the movie takes place and 4 years after The Ramones broke up.
In the subway scene where Taxi is waiting for a train, a train which is shown passing by is a modern NYC transit train. NYC subway trains in the 70s did not have digital train information on the sides of the cars.
In just about every 'live performance' scene there are more audible vocalists than can be seen, and in some cases studio effects are used on the vocals that would have been impossible to recreate live at that time using that venue's equipment (stereo chorus/flanging, etc)
When "The Police" perform Roxanne for Hilly, the studio version is used, complete with the infamous sound of Sting accidentally sitting on a piano during the recording at the beginning of the track. They edited out his laugh afterward but did not edit out the piano chord.